1. Field of the Invention
The present invention relates to the field of computer systems. More specifically, the present invention relates to the art of detecting power supply loss in a microprocessor system.
2. Description of the Related Art
Digital systems are sensitive to power supply perturbations. Power outages or momentary losses of power (i e., voltage brownouts) can cause microprocessor systems, such as computers, to reset (i.e., reboot). There are typically other reasons for resetting a microprocessor system. For example, the user might reboot the system by pressing a predetermined key combination on the keyboard (soft reboot), or by pressing a reset switch (hard reboot). Also, certain software applications may reset the computer due to changes made in the operating environment that require the system to be reset prior to becoming effective.
When the system reboots, the user might want the computer to operate differently depending on the reason for the reboot. For example, if the user were to be away from the computer and power was lost, they might want the computer to remain off. On the other hand, if the reboot was caused intentionally by a software application, the user would desire that the computer would restart.
To ensure proper operation following a power loss event, microprocessor systems typically include power loss detection and reset signal generation circuitry. Known methods for detecting power supply loss includes monitoring a memory cell or a resistor/capacitor (RC) network. These methods require additional capacitors, resistors, and a memory cell (e.g., DRAM, J-K flip flop) to implement, thus increasing the board surface area and resultingly, the cost of the system.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above by providing a novel and nonobvious method and apparatus for detecting the loss of power supply voltage.